Method of forming reusable seamless mandrels for the fabrication of hollow fiber wound vessels

ABSTRACT

A method for fabricating, and a resulting structure for, a seamless, reusable and collapsible mandrel suitable for forming a plurality of seamless and hollow fiber wound vessels upon is disclosed. A destructible mandrel is used to form the seamless reusable mandrel. The destructible mandrel is preferably formed from a material which can be destroyed by dissolving, for example, materials such as foam or plaster. The seamless, collapsible, and reusable mandrel includes a plurality of different layers including a gas impermeable layer, a continuous fiber wound layer, and a release surface forming the outermost layer of the seamless, collapsible, and reusable mandrel. The resulting seamless, reusable and collapsible mandrel has advantages over mandrels which include a seam. Such advantages include a longer useful life and consistently high quality fiber wound vessels at a relatively low cost.

This application is a divisional of application Ser. No. 07/909,045filed Jul. 6, 1992.

BACKGROUND

1. The Field of the Invention

The present invention relates to mandrels used for fabricating hollowcontinuous filament wound vessels and tanks and methods of constructingsuch mandrels.

2. The Prior Art

Methods of constructing filament wound vessels, tanks, and containersare well known in the prior art. Typically, a rigid mandrel made ofaluminum, fiberglass, or other high strength and relatively lightweightmaterial, or the like is prepared and mounted on a filament windingmachine so that the mandrel may be selectively rotated. The surface ofthe mandrel is coated with an appropriate mold release preparation andthen wound with resin impregnated or coated filaments, such as glass,KEVLAR®, graphite, nylon or boron fibers. Commonly, the windingprogresses from end to end for an elongated shape or from side to sidefor a more spherical shape. When the desired thickness of the windinglayers is achieved, the winding is stopped and the resin is cured.

In many cases, the resulting filament wound vessel is removed from themandrel by cutting the vessel about its circumference, generally at alocation near the center thereof. The two halves of the vessel are thenremoved from the mandrel and the halves joined and bonded together toform the desired vessel or tank. A short helical wind of a resin coatedfilament strand or roving may be made over the joint of the vessel in anattempt to further secure the two halves together.

Examples of prior art winding techniques and methods are disclosed inU.S. Pat. Nos. 3,386,872, 3,412,891, 3,697,352, 3,692,601, 3,533,869,3,502,529 and 3,414,449.

Because of the joint in the completed vessel, an inherent weaknessexists which may be the first to fail or fracture when the completedvessel is subjected to pressure or stress. Because of the weakness inthe resulting vessel and the added labor costs associated with cuttingthe vessel and rejoining the two halves of the vessel, techniques havebeen developed which allow the fabrication of hollow vessels without theneed to cut the vessel to remove it from the mandrel.

In some cases, for example, a hollow mandrel is designed to become anintegral part of the completed fiber wound vessel. Disadvantageously,the intended use of the completed fiber wound vessel is often notcompatible with retaining the mandrel as the interior of the vessel.Another technique involves using a mandrel which is destroyed once thevessel is formed. It will be appreciated that if a large number of aparticular configuration of fiber wound vessel are to be fabricated,destroying the mandrel with each use is an exorbitantly expensivetechnique. Thus, reusable mandrels have been developed.

In some cases, segmented metal mandrels, which can be disassembled intosmall sections and then removed through an opening in the completedvessel, have been used. Disadvantageously, building a reusable metalmandrel is costly and time consuming. The difficulty of building areusable segmented metal mandrel makes it too expensive for all but themost demanding applications of high volume vessel fabrication.

Another type of mandrel which has been used to produce seamlesscompleted fiber wound vessels is a collapsible mandrel. Collapsiblemandrels are hollow mandrels made of flexible, air tight materials suchas a rubber which can be inflated while the vessel is being formedthereon and then deflated and removed through an opening in thecompleted vessel.

One collapsible mandrel which can be removed through an opening in acompleted vessel is disclosed in U.S. Pat. No. 4,684,423 to Brooks.While the method of forming the mandrel and, the resulting mandrelstructure, which are disclosed in the Brooks reference represented agreat advance in the art, several disadvantages still remain. The Brooksreference requires that the resulting mandrel be cut in half to removeit from a rigid mandrel. Cutting and splicing the mandrel structureresults in an inherently weaker and less desirable mandrel. Since thearea at the resulting joint is weaker than the remaining structure, thejoint often fails sooner than the other portions of the structure. Thus,the usable life of the mandrel is often unduly limited because of thepresence of the joint.

Further drawbacks and disadvantages inherent in the structure and methoddisclosed in the Brooks reference include the additional labor which isrequired to cut and rejoin the mandrel. Moreover, since the outsidesurface of the mandrel determines the shape and uniformity of theinterior surface of the completed fiber wound structure, a poorly formedseam in the collapsible mandrel can result in an inconsistent surface inthe completed fiber wound hollow structure. Even though the use ofcollapsible mandrels to form seamless completed structures is known, forexample as in the Brooks reference, the problems inherent in a mandrelwhich has been cut and spliced together has not been addressed in theart.

In view of the forgoing, it would be an advance in the art to provide aseamless, collapsible, and reusable mandrel structure and anaccompanying method of forming the same.

BRIEF SUMMARY AND OBJECTS OF THE INVENTION

In view of the above described state of the art, the present inventionseeks to realize the following objects and advantages.

It is a primary object of the present invention to provide a collapsiblemandrel which is suitable for use in the fabrication of filament woundvessels and which is seamless, as well as, an accompanying method ofmaking the same.

It is also an object of the present invention to produce an improvedcollapsible mandrel which is suitable for use in the fabrication offilament wound vessels which maintains its proper shape as the vessel isfabricated upon it, as well as, an accompanying method of making thesame.

It is also an object of the present invention to provide an improvedcollapsible and reusable mandrel upon which high quality filament woundvessels can be consistently produced.

It is another object of the present invention to provide a collapsibleand reusable mandrel which has a long useful life and which can befabricated at a relatively low cost.

These and other objects and advantages of the invention will become morefully apparent from the description and claims which follow, or may belearned by the practice of the invention.

The present invention provides a method for fabricating, and a resultingstructure for, a seamless, reusable and collapsible mandrel suitable forforming a plurality of seamless and hollow fiber wound vessels upon. Themethod of fabricating the seamless reusable mandrel includes readying adestructible mandrel upon which the seamless reusable mandrel is formed.The destructible mandrel is the general shape of the seamless mandreland is preferably formed from a material which can be destroyed bydissolving the material, for example, materials such as foam or plaster.

The structure of the seamless, collapsible, and reusable mandrel of thepresent invention includes a plurality of different layers, each layerhaving a particular function. Different embodiments of the presentinvention require different numbers of layers in the seamless,collapsible, and reusable mandrel. Exemplary of the layers which arelaid upon the destructible mandrel to fabricate the seamless,collapsible, and reusable mandrel of the present invention include: afirst layer of generally fluid impermeable material; a second layer ofcontinuous fibers wound about the destructible mandrel; and a layerwhich functions as a release surface forming the outermost layer of theseamless, collapsible, and reusable mandrel of the, present invention.The release surface is formed in the shape of the interior of thecompleted seamless and hollow fiber wound vessel which will be formed onthe seamless, collapsible, and reusable mandrel. The outer surface ofthe seamless, collapsible, and reusable mandrel is preferably machinedso that it exactly matches the desired shape of the interior of acompleted fiber wound hollow vessel to be formed thereon.

The destructible mandrel is removed from the interior of the seamless,reusable and collapsible mandrel preferably by dissolving the materialfrom which the destructible mandrel is formed. Thus, the integrity ofthe seamless, collapsible, and reusable mandrel is not disturbed by aseam. Previously available mandrels, which needed to be cut in half andspliced back together to remove them from the rigid mandrel upon whichthey were formed, are inherently weaker and less desirable than theseamless mandrels produced by the present invention.

The seamless, reusable and collapsible mandrel of the present inventionincludes at least means for conducting a gas under pressure to theinterior of the mandrel and a fluid impermeable layer capable ofretaining a gas within the interior of the mandrel. Also included is afiber reinforcement layer capable of limiting the expansion of themandrel when pressurized gas is introduced therein such that as thepressure inside the mandrel is . increased and the material forming thevessel is added to the outer surface of the reusable and collapsiblemandrel, the mandrel maintains its desired shape. The fiberreinforcement layer is formed using continuous fiber winding techniques.Also included is an outer release surface. The outer release surf acereceives the materials of the seamless and fiber wound hollow vesselformed thereon. The seamless, reusable and collapsible mandrel of thepresent invention can be reused many times and consistently produceshigh quality fiber wound vessels at a relatively low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to better appreciate how the above-recited and other advantagesand objects of the invention are obtained, a more particular descriptionof the invention briefly described above will be rendered by referenceto a specific embodiment thereof which is illustrated in the appendeddrawings. Understanding that these drawings depict only a typicalembodiment of the invention and are not therefore to be consideredlimiting of its scope, the invention will be described and explainedwith additional specificity and detail through the use of theaccompanying drawings in which:

FIG. 1 is a partially cut away perspective view of the presentlypreferred embodiment of the completed seamless, collapsible, andreusable mandrel of the present invention.

FIG. 2 is a cross sectional view of the mandrel of the present inventionas it appears when mounted on a winding machine shaft ready to receivethe filament windings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made to the drawings wherein like structures willbe provided with like reference designations.

It will be appreciated that as the number and kinds of applications forfilament wound hollow vessels increases, the demand for easilyfabricated, precision mandrels has also increased. The present inventionprovides the benefits of low cost which accompany the use of seamedinflatable mandrels as well as the added benefits of precision and longlife which, prior to the present invention, only accompanied the use ofsegmented metal mandrels.

Reference will now be made to the presently preferred seamless,collapsible, and reusable mandrel generally represented at 100 shown ina partially cut away perspective view in FIG. 1. The seamless,collapsible, and reusable mandrel 100 represented in FIG. 1 isfabricated using known materials and techniques in conjunction withinventive teachings set forth herein. Those skilled in the pertinentarts will readily recognize the materials and techniques describedherein are also of the general type and class referred to in U.S. Pat.No. 4,684,423 to Brooks which is now incorporated herein by reference.

FIG. 1 represents the various structural layers of the seamless,collapsible, and reusable mandrel 100 of the present invention. Whilethe mandrel 100 illustrated in FIG. 1 is of a cylindrical shape, themandrels of the present invention can be fabricated into any number ofshapes needed to form hollow vessels.

The steps set forth below are presently preferred for fabricating theseamless, collapsible, and reusable mandrel 100 illustrated in FIG. 1.

A non-reusable mandrel 90 is first fabricated, on a shaft 92, upon whichthe seamless, collapsible, and reusable mandrel 100 will be fabricated.The non-reusable mandrel 90 is only partially represented in phantomimage in FIG. 1 to show its relationship to the seamless, collapsible,and reusable mandrel 100. The shape of the non-reusable mandrel willdetermine the shape of the seamless, collapsible, and reusable mandrel100. Utilization of a non-reusable mandrel is essential to the presentinvention in order to fabricate the resulting reusable collapsiblemandrel 100 as a seamless mandrel. Such a non-reusable mandrel must bedestroyed during use in order to remove the resulting seamless mandrel.Thus, such a mandrel is also referred to herein as a destructiblemandrel.

The non-reusable mandrel 90 can be formed from many different materialsand procedures; those skilled in the art will realize that the hereindescribed materials and procedures are merely preferred and that othermaterials and procedures can also be used. The important criteria isthat the resulting mandrel 90 must be readily destructible in order toremove it from the small polar opening, 112 in FIG. 1, which remains inthe seamless, collapsible, and reusable mandrel 100.

To form the mandrel 90, it is preferred that a foam block be set up on ashaft 92 and formed using a turning mechanism. The foam block should beformed to slightly smaller than a shape which conforms to the finishedshape of the non-reusable mandrel 90.

A screeding template is formed which conforms exactly to the finishedshape and size of the non-reusable master mandrel 90. The screedingtemplate is set to the proper orientation on the turning mechanism. Amixture consisting of 80% plaster and 20% milled glass fibers (1/32 inchto 1/4 inch) is prepared. The plaster is preferably one which is readilydissolved or destroyed such as that available under the trademark EASYOUT.

While the foam block is rotated on the shaft turning mechanism, glasscloth strips (7500 style or equivalent) and plaster is laid on the foamblock. After a first layer of glass cloth strips and plaster has dried,a further layer(s) of glass cloth strips and plaster is added until thesurface is about 1/4 inch from the surface of the screed. After theprevious layers of cloth and plaster have hardened a final layer of onlyplaster is added using the screeding template to form the surf ace tothe exact shape and size desired. The non-reusable mandrel 90 is thenallowed to dry for 24 hours.

After the non-reusable mandrel 90 is dried, it is preferably cured at300° F. to 600° F. for two hours for each inch thickness of plastermixture added to the surface of the foam block. Upon completion of thecure time, the non-reusable mandrel 90 should be cooled at a rate notexceeding, 5° F. per minute. The non-reusable mandrel 90 should then beinspected and any rough areas smoothed with a fine grit sand paper asrequired. The surface of the non-reusable mandrel 90 is then sealingwith any appropriate resin, tape, or soluble liquid sealant which willprovide a suitable release surface for the non-reusable mandrel 90.

The completed non-reusable mandrel 90 is mounted on a 3-axis windingmachine having a fiber delivery system as is known in the art. With thesurface of the non-reusable master mandrel prepared with a releasematerial, an inner rubber layer 102 of uncured rubber is applied usingmethyl-ethyl-ketone (MEK) sparingly as a tackifier. The sheet of rubbershould be trimmed so that the sheets overlap by at least 1/8 inch. Therubber sheets will need to be trimmed so that the rubber lies evenly onthe contours of the non-reusable master mandrel.

A dispersion solution is prepared and used next. The dispersion solutionpreferably comprises small bits of nitrile sheet which have been soakedin MEK for at least 1 hour with mixing until the bits are well dissolvedand the solution is the consistency of paint. This dispersion solutionwill be used for encapsulating the Kevlar fiber during winding. Thedispersion solution should be agitated and thinned with MEK as needed toavoid clumping.

The winding machine should be programmed to the required specificationsas is known in the art. As is known in the art, the lowest angle helicalis normally wound first to create helical fiber plies as represented atfiber wound layer 104 in FIG. 1. The resulting fiber band should be in a"space wind" configuration with a minimum of 1/8" spacing between tows.

After the first helical winding is completed, the nitrile/MEK solutionshould be allowed to outgas at room temperature for at least 20 minutes.The winding machine can be used to apply winding angles in addition tothe first helical winding to further complete the helical fiber pliescomprising the fiber reinforced layer 104. Care should be exercised toavoid bridging the rubber layers between the fibers in order to achievea strong rubber-to-rubber bond. In the case of small, seamless,collapsible, and reusable mandrels, both a hoop and helical ply may beneeded together at this point for the helical fiber plies 104 to havethe desired characteristics. Next, if desired, the winding machine canbe programmed to wind another helical layer.

After the helical plies have been completed to form the fiber reinforcedlayer 104, a first middle rubber layer 106 of uncured rubber is appliedin a manner the same as or similar to that described for the innerrubber layer 102. As indicated earlier, the rubber sheets should betrimmed so that the sheets overlap so that the rubber lies evenly on thecontours of the non-reusable mandrel 90.

The winding machine should next be programmed to the hoop windingprogram to form another fiber reinforced layer 108, this time using ahoop fiber ply as represented in FIG. 1 and as indicated earlier. Thehoop fiber ply, forming another fiber reinforced layer 108 is wound fromtangent to tangent and, upon completion, the nitrile/MEK solution shouldagain be allowed to outgas at room temperature for at least 20 minutes.

Next, a second middle layer of rubber 114 is laid on as describedearlier followed by the winding machine being programmed and executing ahigh angle helical wind forming a second fiber reinforced layer 116.Following the completion of the winding, the structure is outgassing atroom temperature for at least 20 minutes. If desired, additional fiberreinforced layers (e.%., hoop or tangent windings) and rubber layers canbe added to the mandrel 100 of the present invention followed by theoutgassing steps.

Next, the outer rubber layer 110 is applied as indicated in the earlierdescribed steps. If desired, extra sheets of rubber can be applied tothe outer rubber layer 110 to serve as a sacrificial machining layer.The surface of the outer rubber layer 110 will function as a releasesurf ace in the shape of the interior of the completed fiber woundhollow vessel. If needed, material such as glass cloth strips (7500style or equivalent) can be used to reinforce the outer rubber layer 110as required to achieve added strength and/or rigidity.

The entire seamless, collapsible, and reusable mandrel is next wrappedin perforated TEDLAR® release film. The seamless, collapsible, andreusable mandrel is then preferably enveloped in a nylon vacuum bagequipped with an N-10 breather as is known in the art. Importantly, itshould be assured that the interior of the seamless, collapsible, andreusable mandrel is evacuated. The greatest vacuum available should beapplied to the seamless, collapsible, and reusable mandrel at roomtemperature for best results. Checks should be made to detect any leaks.

Next, the bagged seamless, collapsible, and reusable mandrel is cured at350° F. for 2 hours (minimum) or cured in accordance with the rubbermanufacturer's recommendations. A lower temperature hold is permissible,if desired. Preferably, an autoclave (capable of pressures of at least30 p.s.i.g.) should be used but internal pressure or thermal compactiontechniques, as known in the art, may also be employed.

After the cure time is complete, the seamless, collapsible, and reusablemandrel is allowed to cool down slowly and the bagging material isremoved. After the bagging material is removed, the seamless,collapsible, and reusable mandrel should be trimmed in the appropriateareas. The non-reusable mandrel 90 should then be removed. Preferably,the non-reusable mandrel 90 is removed by destroying it and removing theresulting slurry and/or pieces through the small polar opening 112. Anultrasonic knife or very sharp trimming tools should be used to cutKevlar.

After the seamless, collapsible, and reusable mandrel 100 is free fromthe non-reusable mandrel 90 and finished, it should be mounted onto awinding shaft with all of its associated hardware (see FIG. 2) to verifythat the seamless, collapsible, and reusable mandrel 100 is concentricto the shaft with very little runout (preferably less than 0.020 inch).A leak check at 2 p.s.i. minimum should also be performed.

The outside of the seamless, collapsible, and reusable mandrel should bemachined as necessary to contour the outer rubber surface. Inpreparation for fabricating a fiber wound filament vessel on theseamless, collapsible, and reusable mandrel, a 1-2 mil thick FEP releaselayer (as known in the art) can be sprayed onto the outer rubber layer110, if required. Further inspection of the mandrel 100 using templates,ω tape, and dial indicators should be performed to ensure consistentquality.

FIG. 2 is a diagrammatic cross sectional view of the seamless,collapsible, and reusable mandrel 100 mounted on a hollow winding shaftS commonly found in a winding machine (not shown) as known in the art.The winding shaft includes a passageway A which conducts a gas underpressure to the interior of the seamless, collapsible, and reusablemandrel 100.

The seamless, collapsible, and reusable mandrel 100 is held in place onthe winding shaft S by a polar boss 118, which will become part of thecompleted fiber wound hollow vessel (not shown), and various pieces ofhardware 120 which retain the polar boss 118 and grasp the winding shaftS. Such structures can be those which are known in the art.

With the seamless, collapsible, and reusable mandrel 100 mounted on thewinding shaft S, the fiber wound hollow vessel is formed thereon. Asmore material is added to the mandrel 100, the pressure within theseamless, collapsible, and reusable mandrel 100 is adjusted to maintainthe proper shape of the mandrel 100. When the fiber wound hollow vessel(not represented) is completed, the mandrel 100 is deflated and thehardware 120 removed, and the mandrel 100 removed through the endopening of the completed fiber wound hollow vessel (not shown).

Since the mandrel 100 is seamless, it is inherently stronger than acorresponding mandrel which was cut and spliced while being formed.Thus, the mandrel 100 is reusable many times more than similar mandrelshaving a seam. Moreover, the represented seamless mandrel 100 is capableof producing more uniform completed fiber wound hollow vessels.

It will be appreciated that the present invention provides a collapsiblemandrel which is suitable for use in the fabrication of various filamentwound hollow vessels and which is seamless. The present invention alsoproduces an inflatable mandrel which maintains its proper shape as ahollow vessel is fabricated upon it as well as being reusable toconsistently fabricate high quality filament wound hollow vessels andwhich is relatively low cost.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

What is claimed and desired to be secured by United States LettersPatent is:
 1. A reusable and collapsible mandrel suitable for formingseamless and hollow fiber wound hollow vessels upon, the mandrelcomprising:means for conducting a gas under pressure to the interior ofthe mandrel; a first gas impermeable layer capable of retaining a gaswithin the interior of the mandrel; at least a first fiber reinforcementlayer, comprising a low angle helical wind ply, capable of limiting theexpansion of the mandrel when pressurized gas is introduced therein suchthat as the pressure inside the mandrel is increased as the materialforming the vessel is added to the outer surface of the reusable andcollapsible mandrel, the mandrel maintains its desired shape; a secondgas impermeable layer capable of retaining a gas within the interior ofthe mandrel; a second fiber reinforcement layer, comprising a hoop windply, capable of limiting the expansion of the mandrel when pressurizedgas is introduced therein such that as the pressure inside the vessel isincreased the mandrel maintains its desired shape; and an outer releasesurface providing a surface to receive the materials of the seamless andhollow fiber wound hollow vessel formed thereon, the outer releasesurface means formed exteriorly of the gas impermeable layers and thefiber reinforcement layers, the gas impermeable layers and fiberreinforcement layers all being formed without any seams and such thatthe reusable and collapsible mandrel can be removed from a completedseamless and hollow fiber wound hollow vessel and be reused to form aplurality of seamless and hollow fiber wound vessels.
 2. A reusable andcollapsible mandrel suitable for forming seamless and hollow fiber woundhollow vessels upon as defined in claim 1 wherein the first and secondgas impermeable layer comprises a rubber layers.
 3. A reusable andcollapsible mandrel suitable for farming seamless and hollow fiber woundhollow vessels upon as defined in claim 1, wherein the outer releasesurface comprises a rubber layer.
 4. A reusable and collapsible mandrelsuitable for forming seamless and hollow fiber wound hollow vesselscomprisingmeans for conducting a gas under pressure to the interior ofthe mandrel; an inner gas impermeable layer having an outer surface,said layer capable of retaining a gas within the interior of themandrel; a first fiber reinforcement layer, having an outer surface,disposed on the outer surface of the inner gas impermeable layer, saidfirst fiber reinforcement layer capable of limiting the expansion of themandrel when pressurized gas in introduced therein such that as thepressure inside the mandrel in increased as the material forming thevessel is added to the outer surface of the reusable and collapsiblemandrel, the mandrel maintains its desired shape, wherein said firstfiber reinforcement layer consists of a low angle helical wind ply in aspace wind configuration such that there is a minimum of one-eighth inchspacing between tows and optionally one or more additional fiber plieshaving winding angles selected from the group consisting of hoop andhelical winds; a first middle gas impermeable layer disposed on theouter surface of the first fiber reinforcement layer, said first middlegas impermeable layer having an outer surface and being capable ofretaining a gas within the interior of the mandrel; a second fiberreinforcement layer disposed on the outer surface of the first middlegas impermeable layer, said second fiber reinforcement layer beingcapable of limiting expansion of the mandrel when pressurized gas inintroduced therein such that as pressure inside the mandrel inincreased, the mandrel maintains its desired shape, wherein said secondfiber reinforcement layer comprises a hoop wind ply and has an outersurface; a second middle gas impermeable layer disposed on the outersurface of the second fiber reinforcement layer, said second middle gasimpermeable layer being capable of retaining a gas within the interiorof the mandrel and having an outer surface; a third fiber reinforcementlayer capable of limiting expansion of the mandrel when pressurized gasis introduced therein, wherein said third fiber reinforcement layercomprises a high angle helical wind ply; an outer gas impermeable layercapable of retaining a gas within the interior of the mandrel andoptionally containing additional layers of gas impermeable material forforming sacrificial machining layers so that the desired surface of themandrel is obtained, and optionally containing additional reinforcementmaterial; and an outer release layer providing a surface to receive thematerials of the seamless and hollow fiber wound hollow vessel formedthereon, the outer release surface formed exteriorly of the outer gasimpermeable layer and fiber reinforcement layers, the gas impermeablelayers and fiber reinforcement layers all being formed without any seamsand such that the reusable and collapsible mandrel can be removed from acompleted seamless and hollow fiber wound hollow vessel and be reused toform a plurality of seamless and hollow fiber wound vessels.
 5. Thereusable and collapsible mandrel of claim 4 wherein the reinforcementmaterial of the outer gas impermeable layer is glass cloth.
 6. Thereusable and collapsible mandrel of claim 4 wherein one or moreadditional fiber reinforcement layers and gas impermeable layers aredisposed on the mandrel exteriorly of the third fiber reinforcementlayer and interiorly of the outer gas impermeable layer.